This invention relates to a novel method of applying a film of reduced light transmittance to the interior surface of a contoured car window.
In many regions of the United States, the intensity of the sunlight and the glare resulting therefrom have been found to be notable factors in causing motor vehicle accidents. The tinting of windows by the vehicle manufacturer has provided a measure of relief to the operator. In addition, the tinting of the windows reduces the damage to the vehicle interior caused by strong incident light over a long period of time. However, the need has been recognized for additional means of reducing the combination of direct and reflected light entering a vehicle. To this end, a number of manufacturers now provide plastic film for placement on car windows. The films are characterized by reducing the amount of light transmitted therethrough in both the visible and invisible spectral regions. Typically, commercially available films exhibit substantial blocking characteristics for light having a frequency in the ultraviolet portion of the spectrum.
The reduced light transmissive films are generally made with an adhesive layer provided on one side of a plastic film with a removable plastic transfer coating thereon. The transfer coating is removed at the time of installation to permit adherence of the film to the window surface. Since the film is less durable than the glass substrate, the application of the film to a vehicle window takes place on its interior surface where it is protected from the weather. As a result, the customary procedures for adhering film to the window are difficult to perform. The difficulty is due to the fact that the operator is applying flexible film to the windows from a position within the vehicle. Considerable skill is required for a successful application. As a result, the vehicle owner is not normally capable of satisfactorily applying the film. Commercial establishments specializing in the application of films to vehicle windows have come into existence to satisfy this commercial need.
The typical approach to applying a plastic film begins with the initial placement of a combination of film and transfer coating thereon against the surface of the window. This outlines the dimension of the film to be applied and it is then cut to size. Following the dimensioning, the transfer coating is removed to expose the adhesive layer. The layer on the film is then placed in direct contact with the interior surface of the car window. The process works reasonably well with installations wherein flat glass surfaces serve as the substrate. However, present day vehicles rarely have flat glass windows. Virtually every window on today's vehicles is contoured for aesthetic and/or aerodynamic purposes, thereby rendering the application of the film more difficult. In addition to the fact that vehicle windows are now contoured, recent styling changes have greatly increased the area of the contoured windows especially rear windows in those models having sloping or hatch backs. Applying the film to the larger areas of contoured windows makes the process of conforming the film to the interior window surface even more difficult. In order to successfully deal with the large area contoured window, it is standard practice to divide the window into a plurality of segments and then to apply the film in pieces. By subdividing the film, it is easier to provide large area coverage from the car interior.
In the case of both unitary or segmented film applications, the conventional practice is to apply tension to the film to alter its original dimensions. The stretching of the film is used in conforming the film to the window surface. Stretching eliminates for the most part the buckles, fingers and creases that arise from the placement of a flat film on a curved window surface. As a result of the film being stretched, the adhesive layer, placed on the film initially as a layer of uniform thickness, becomes thinner in the regions stretched. Since the stretching most often occurs at those areas where the window contour undergoes a significant change, the adhesive layer becomes thinned in the region where the film is most severely stressed. These regions are the areas where the film is most likely to undergo a later separation from the glass substrate. As a result, film stretching during installation materially reduces the useful lifetime of the installed product.
One approach taken to limit the amount of film stretching is to segment the plastic film prior to application. However, the segmenting of the film results in seams extending across the window. Applying multiple segments calls for increased care and effort to ensure that the segments directly abut one another over the long dimensions. Any gaps, overlaps or edge-raising will be prominently displayed leading to customer dissatisfaction and impairment of an otherwise unobstructed view. Furthermore, the dimensional changes that the film undergoes over a period of time promotes the formation of gaps right across the long dimension of the window. This is both unsightly and potentially dangerous if the sun rays passing through the crack are directed onto the face of the driver.
Accordingly, a primary object of the present invention is the provision of a method for installing window film which reduces the number of steps required to cover a contoured window by essentially eliminating the need to treat the window in segments. The invention reduces the need to stretch the film which normally produces localized reductions in the adhesive layer. Consequently, the useful lifetime of the applied film is increased. The present method can be used to eliminate the transverse seams heretofore existing in plastic film applied to large area contoured windows.